Living polymerization allows for the synthesis of new polymers and oligomers with controlled molecular weight distribution and with specialized functional substituents. Recent advances have occurred in the polymerization by cationic mechanisms to yield living polymers where living polymer characteristics were not previously obtained due to the reactivity or instability of the compositions involved.
T. Higashimura and M. Sawamoto; Adv. Polym. Sci.,
1984, 62, 50-94, review the attempts at living cationic polymerization of vinyl monomers and state that until recently it was considered "beyond our reach." They disclose the use of an HI/I.sub.2 initiating system to polymerize isobutyl vinyl ether in n-hexane. They claim this polymerization system to be the first example of living cationic polymerization of vinyl compounds.
M. Miyamoto, M. Sawamoto, and T. Higashimura; Macromol 1984, 17, 265-268 show that living polymerization of isobutylvinyl ether using HI/I.sub.2, I.sub.2, or HI as initiators, does not occur in a polar solvent such as CH.sub.2 Cl.sub.2.
S. Aoshima and T. Higashimura; Polym. Bull., 1986, 15, 417-423, disclose the use of esters as Lewis base modifiers for EtAlCl.sub.2. These systems are used as initiators for the living cationic polymerization of vinyl ethers.
T. Higashimura, Y. Kishimoto, and S. Aoshima; Polym. Bull., 1987, 18, 111-115 disclose the use of an EtAlCl.sub.2 /dioxane initiating system for the living cationic polymerization of vinyl monomers.
R. Faust and J. P. Kennedy; Polym Bull., 1986, 15, 317-323, describe the living carbocationic polymerizations of isobutene using initiating complexes of organic esters with Lewis acids.
EP 206,756, discloses the use of complexes of Lewis acids and organic acids or esters as catalysts for the living polymerization of olefins and diolefins.
JP J6 0228-509, discloses the preparation of polyalkenyl ethers by living polymerization using as catalysts iodine and optionally HI.
U.S. Pat. No. 4,393,199 discloses a method of polymerizing monomers capable of cationic polymerization by using an adduct consisting of a preinitiator precursor and a catalyst, to react with the monomer and produce a polymer of low polydispersity.
U.S. Pat. No. 4,696,988 discloses the use of HI/I.sub.2 initiating systems to polymerize isopropenylphenyl glycidyl ethers.
F. Bolza et al., Makromol Chem., 1980, 181, 839, disclose the polymerization of isobutyl vinyl ether with trifluoroacetic acid in methylene chloride and carbon tetrachloride in the range of -2.5.degree. to 35.degree. C. Their results do not support a living polymerization mechanism.
H. Shohi et al., Polym. Bull , 1989, 21, 357, disclose that an adduct of trifluoroacetic acid to an alkyl vinyl ether can be used for living polymerization of alkyl vinyl ethers, using ethylaluminium dichloride as a catalyst. In this case, the presence of 1,4-dioxane in the polymerization solvent is absolutely necessary for living polymerization in order to stabilize the growing chain end.
S. Aoshima et al., Macromol.,1989, 22, 1009, disclose that polymerization of alkylvinyl ether with trifluoroacetic acid or an adduct of acetic acid and an alkyl vinyl ether as an initiator and ethylaluminium dichloride as a catalyst. As above the presence of a Lewis base, ethyl acetate, in the solvent is absolutely necessary for living polymerization in order to stabilize the growing chain end.
The above described art shows that living cationic polymerization requires either a cosolvent as a stabilizer or a unique combination of an initiator/catalyst.
It is difficult to predict which initiator/catalyst combinations will result in a living cationic polymerization of a vinyl monomer. For example, S. Aoshima and T. Higashimura, op. cit., show that living polymerizations of 2-vinyloxyethyl benzoate and 2-vinyloxyethyl methacrylate monomers, where the ester functioning as a Lewis base is incorporated within its structure, can be conducted using EtAlCl.sub.2 but not with BF.sub.3 OEt.sub.2.
The present invention provides a process for the cationic polymerization of vinylic unsaturated compounds using a mixture of a halogenated acid and a zinc salt of a halogenated acid as an initiator and catalyst respectively.